// defined constants: calculate circumference

#include <iostream>
using namespace std;

#define PI 3.14159
#define NEWLINE '\n'

int main(int argc, char const *argv[])
{
	double r=5.0;
	double circle;

	circle = 2 * PI * r;
	cout << circle;
	cout << NEWLINE;

	return 0;
}